Internal combustion engines use only a portion (for example, approximately 31% to 38% in some cases) of the supplied fuel energy due to heat wasted, friction, incomplete combustion, and others. In addition, approximately 3-17% of the supplied fuel energy can be used to maintain the engine operation during standby and another 1-2% can be used to operate accessories. Therefore, it can be advantageous to utilize the waste energy, typically in the form of thermal and chemical energy, to improve the overall vehicle system fuel efficiency.
One approach uses a fuel cell arranged in an exhaust system of an internal combustion engine, such as described in U.S. 2004/0177607 (“the '607 reference). This system uses unburnt fuel from the engine to convert chemical energy into electric energy that can be used in vehicle. The system includes various exhaust gas sensors separate from the fuel cell, such as air-fuel ratio sensors for controlling operation. Further, the '607 reference describes operating the engine independently of the conditions of the fuel cell.
The inventors herein have recognized that while separate air-fuel ratio sensors may be used, it is also possible, at least under some conditions, to use a fuel cell to provide information that can be used in controlling or adjusting engine operation. For example, the conditions of the fuel cell may be used to determine, estimate, or provide information about the air/fuel ratio or relative oxygen amount in the exhaust. Thus, it may be possible to use the current, voltage, and/or impedance of the fuel cell to provide an indication of the exhaust air-fuel ratio, or other conditions of the exhaust.
Thus, according to one aspect, a system for a vehicle having an engine with an exhaust comprises a fuel cell coupled in the engine exhaust wherein the fuel cell has an output circuit; a battery coupled with the fuel cell; and a controller receiving a signal indicative of an electric output of the fuel cell output circuit, and adjusting one of the fuel amount and the air amount supplied to the engine in response to said signal to affect air-fuel ratio of the exhaust of the engine
In this way, the electrical output of the fuel cell can be used as an indication of exhaust information, such as exhaust air/fuel ratio, and then be used to adjust engine operation. For example, the fuel cell can operate as a Nerst cell in one embodiment.
Thus, in one embodiment, it may be possible to reduce a number of exhaust air-fuel ratio sensors, thus reducing system cost. In another embodiment, the fuel cell can be used as an additional air-fuel ratio sensor to supplement other air-fuel ratio sensor information. Further, in some examples, the fuel cell output can be used to determine degradation of the fuel cell and/or of other exhaust air-fuel ratio sensors. Therefore, the fuel cell may serve multiple functions such as power generation, sensing, and/or diagnosis.
According to another aspect, a method to operate an internal combustion engine of a vehicle, the engine also includes a fuel cell disposed downstream of the engine coupled in an engine exhaust and a battery coupled with the fuel cell. The method comprises adjusting an engine operating parameter in response to an electrical output of the fuel cell coupled in the engine exhaust.
In this way, it is possible to take advantage of the fuel cell location and operation to provide information about engine operation, for example, that can then be used in adjusting engine operation.
According to yet another aspect, a method to operate an internal combustion engine of a vehicle, the engine also having a fuel cell disposed at the downstream of the engine and a battery coupled with the fuel cell, is provided. The method comprises: generating an electrical output of the fuel cell by controlling current supplied to the fuel cell from the battery; and adjusting an engine operating parameter in response to said electrical output of the fuel cell.
Such system can provide various advantages. For example, application of the current to the fuel cell allows for generation of an electrical output that may provide information about the exhaust gases, such as air-fuel ratio. For example, in one embodiment, by determining the change in current, it may be possible to infer exhaust air-fuel ratio using the Nernst equation in conjunction with speciation information. Further, applying the current enables an electrochemical reaction that reduces NOx to N2 and O2. Such an approach may enable the fuel cell to serve multiple functions such as power generation, sensing, and/or emission reduction.